Vulcanized rubber products for use in dynamic environment such as driving belts and tires are often subjected to repeated deformation during use and then, generate heat by hysteresis loss (deformation friction loss) inherent to viscoelastomers. The heat generation during use is adverse to energy conservation and leads to shortening of the lifetime of the vulcanized rubber product by high-temperature degradation.
Accordingly, a serious problem to overcome for such vulcanized rubber products is to find a way to prevent heat generation when they are used under dynamic environment. Thus, there were proposed various methods for reduction of the heat generation in vulcanized rubber products, mainly from the material point of view (see, for example, Patent Documents 1 to 4).
Vulcanized rubber products are produced by molding an unvulcanized or semivulcanized rubber composition into a particular shape and vulcanizing the molded article. There was also proposed a two-step vulcanization method for preparation of a vulcanizate in a complicated shape (see Patent Document 5). In the method described in Patent Document 5, an intermediate molded article semivulcanized in the processing-needed region and completely vulcanized in the other region is first prepared, and then after the semivulcanized region of the intermediate molded article is deformed into a desired shape, the intermediate molded article is vulcanized additionally in that state, to give a vulcanizate.
The inventors have found that a styrene butadiene rubber containing silica and a particular silane-coupling agent (TESPT), if post-vulcanized in the state under application of shearing strain after prevulcanization, shows an increased tan δ value in the high-frequency region and a reduced tan δ value in the low frequency region and published the finding earlier (see Nonpatent Document 1).